Batting thermal insulation with fire resistant properties

ABSTRACT

A fibrous thermal insulation comprising an intimate blend of A) an effective amount of non-graphitic carbonaceous fibers having an LOI value greater than 40, a percent char value greater than 65, and a thermal conductivity less than 1 BTU hr ft 2  /°F. for providing a synergistic improvement in fire resistance, and B) hollow thermoplastic fibers.

RELATED APPLICATION

This is a divisional application of Ser. No. 569,678, filed Aug. 20,1990, now U.S. Pat. No. 5,188,896, which is a continuation-in-part ofapplication Ser. No. 554,778, filed Jul. 19, 1990 now U.S. Pat. No.5,188,893 of Suh et al, entitled, "Stabilized and Carbonaceous ExpandedFibers".

FIELD OF THE INVENTION

The present invention relates to lightweight structures that have a highdegree of thermal insulation, are non-wetting and/or buoyant and havegood fire resistance. More particularly, the invention provides alightweight insulation through the use of hollow fibers of thermoplasticmaterial, particularly styrenic fibers, intimately blended with otherfibers and materials, such as carbonaceous polymeric fibers, which canprovide synergistic ignition and fire resistance.

BACKGROUND OF THE INVENTION

It is desirous to have lightweight structures that have a high degree ofthermal insulation that can be washed and dried without retention of agreat amount of water. Fiberglass containing structures are presentlybeing used to provide fiber battings for use in insulating spaces inbuildings and airplanes. In addition, fiberglass battings are being usedas insulation in industrial apparel, blankets and curtains.

The problems with fiberglass is that it is difficult to handle and cancause dermal invitation. Moreover, fiberglass does not have a highinsulation compact value and can pick up moisture so as to cause it tosettle down after installation with a loss in insulation value.

Styrenic fibers are well-known. Moreover, styrenic fibers are low incost, are non-irritating, have good insulation value and can be blendedwith other fibers utilizing conventional processes. The maindisadvantage of styrenic fibers is that they are highly flammable.Hollow styrenic fibers are even more flammable because they provide agreater surface area for combustion.

Hollow fibers can also be prepared from other thermoplastic materialswhich have better fire resistant characteristics than styrene. However,the fire resistance of these thermoplastic materials also decreases whenformulated into hollow fibers.

It is now known that carbonaceous fibers can provide a synergisticimprovement in fire resistance when blended with flammable materials.

U.S. Pat. No. 4,837,076, to McCullough, Jr. et al, which is hereinincorporated by reference, relates to the preparation of non-linearcarbonaceous polymeric fibers and to carbonaceous polymeric fibershaving different electroconductivity. This patent discloses a processwhich can be used to heat treat and carbonize expanded polymeric fibersto yield the fibers of the invention.

U.S. Pat. No. 4,898,783, to McCullough Jr. et al, which is hereinincorporated by reference, discloses the synergism found with a blend ofsolid carbonaceous polymeric fibers and solid thermoplastic fibers.

U.S. Pat. No. 4,752,514, to Windley, which is herein incorporated byreference, discloses crimped and expanded polyamide fibers. The crimpsin the fiber are caused by collapsed portions. There is also disclosed aprocess for preparing precursor fibers useful in the present invention.

U.S. Pat. No. 4,877,093, to Murata et al, which is herein incorporatedby reference, discloses porous expanded acrylonitrile based fibers and aprocess for their preparation. The process can be used for preparing oneof the precursor fibers of the invention.

U.S. Pat. No. 4,832,881, to Arnold Jr. et al, discloses the preparationof low density, microcellular carbon foams from polyamides, cellulosepolymers, polyacrylonitrile, etc. The foams are rigid and brittle.

For the purpose of rendering various terms employed herein clear andreadily understandable, the following definitions are providedhereinafter.

The term "stabilized" herein applies to fibers which have been oxidizedat a specific temperature, typically less than about 250° C. for acrylicfibers. It will be understood that in some instances the fibers areoxidized by chemical oxidants at lower temperatures. The procedure ismore clearly described in U.S. Pat. No. 4,837,076, which is hereinincorporated by reference.

The term "reversible deflection" as used herein applies to a helical orsinusoidal compression spring. Particular reference is made to thepublication, "Mechanical Design--Theory and Practice," MacMillanPublishing Co., 1975, pp 748, particularly Section 14-2, pp 721 to 724as well as the herein before mentioned European published Applicationserial number 0199567.

The term "polymer" or "polymeric material" used herein applies toorganic polymers as defined in Hawley's Condensed Chemical Dictionary,Eleventh Edition, Published by Van Nostrand Rheinhold Company. Theorganic polymers generally include: 1) natural polymers, such ascellulose, and the like; 2) synthetic polymers, such as thermoplastic orthermosetting elastomers; and 3) semisynthetic cellulosics. Polymersincluded herein are also low melting polymeric binders as well aspolymeric fibers.

The term "carbonaceous fibers" as used herein is intended to includelinear or nonlinear carbonaceous fibers, or mixtures of such fibers.

The term "carbonaceous fiber structure" as used herein relates topolymeric fibers whose carbon content has been irreversibly increased asa result of a chemical reaction such as a heat treatment, as disclosedin U.S. Pat. No. 4,837,076, and is at least 65%.

The term "nongraphitic" as used herein relates to those carbonaceousmaterials which are substantially free or oriented carbon or graphitemicrocrystals of a three dimensional order, typically have an elementalcarbon content less than 98% and as further defined in U.S. Pat. No.4,005,183.

The term "ignition resistant" as used herein generally applies to anyone of the characteristics that are referred to as flame arresting,flame retarding, fire shielding and fire barrier, as defined in 14 CFR25.853(b).

An article is considered to be "flame retarding" to the extent that oncean igniting flame has ceased to contact unburned parts of a textilearticle, the article has the inherent ability to resist furtherpropagation of the flame along its unburned portion, thereby stoppingthe internal burning process. Recognized tests to determine whether anarticle is flame retarding are, inter alia, the American Association ofTextile Chemists and Colorist Test Method 34-1966 and the NationalBureau of Standards described in DOC FF 3-71.

An article is considered to be "flame arresting" if it has the abilityto block or prevent flames from contacting unburned parts of a flammablesubstance at least five (5) minutes.

An article is considered to be "fire shielding" if it is capable ofdeflecting flames and the radiation therefrom in a similar manner asaluminum coated protective garments, which are known in the art.

Fire barriers have the characteristic of being nonflammable and flameretarding and also provide thermal insulation characteristics.

The term "polymeric" or "polymeric resin" used herein includes naturalpolymers as well as other organic polymeric resins includingorganosilicone polymers.

The nonlinear carbonaceous fibers preferably used in the invention areresilient, shape reforming and have a reversible deflection greater thanabout 1.2:1. It should be understood that the reversible fiber defectioncomprises two components, pseudoelongation and fiber elongation.Pseudoelongation results from the nonlinear configuration and/or falsetwist imposed on the fiber. Fiber elongation is the elongation to fiberbreak after the fiber has been made linear.

The carbonaceous materials that are suitably employed in the presentinvention have an LOI value of greater than 40 as measured according totest method ASTM D 2863-77. The method is also known as the "oxygenindex" or "limiting oxygen index" (LOI) test. With this procedure theconcentration of oxygen in O₂ /N₂ mixtures is determined at which avertically mounted specimen is ignited at its lower end and justcontinues to burn. The size of the specimen is 0.65×0.3 cm with a lengthof from 7 to 15 cm.

The LOI values of different materials are calculated according to thefollowing equation: ##EQU1##

The carbonaceous materials of the invention are characterized as havinga percentage value greater than 65 and thermal conductivity of less than1 BTU ft/hr ft² °F. The percent char formation and thermal conductivityof various other materials are as follows:

    ______________________________________                                                              Thermal                                                                % Char Conductivity                                            ______________________________________                                        Carbonaceous particles                                                        18.6% N.sub.2    >65      0.1                                                 16.0% N.sub.2    >65      0.2                                                 KEVLAR            60      <1.0                                                KODEL 410 polyester                                                                             10      <1.0                                                Polyacrylonitrile                                                                               60      <1.0                                                Oxidized                                                                      polyacrylonitrile                                                                               60      <1.0                                                THORNEL 300*     >95      4.84                                                Cotton           >30      <1.0                                                Rayon            <50      <1.0                                                Polycarbonate     22      <1.0                                                Polyethylene                                                                  terephthalate     10      <1.0                                                Carbon particles >90      2.5                                                 THORNEL P758**   >95      106.48                                              ______________________________________                                         *Trademark of Amoco Corp., Danbury, CT, for graphite yarn                     **Trademark of Amoco Corp., Danbury, CT, for graphite yarn derived from       pitch.                                                                   

The measurement of char formation as illustrated in the aforementionedtable and as discussed herein is made by using a standardthermogravimetric analysis apparatus that is adapted to perform theanalysis in a nitrogen atmosphere. The apparatus is described inEncyclopedia of Polymer Science, Vol. 14, p. 21, John Wiley & Son, 1971.

The measurement is performed by loading a sample onto a sample pan ofthe thermogravimetric analysis apparatus. The sample is then heated inan nitrogen atmosphere at a rate of 10° C./min from ambient temperatureto 900° C. The thermogravimetric apparatus records the sample weightremaining versus temperature. The percent of original weight remainingat 800° C. is taken as the char percentage.

SUMMARY OF THE INVENTION

The present invention provides a lightweight thermal insulation having ahigh degree of thermal resistance which comprises an intimate blend ofa) an effective amount of non-graphitic carbonaceous polymeric fibersfor providing ignition fire resistance, and b) hollow thermoplasticfibers. The structure advantageously comprises about 20 to 75 percent(%) by weight of the carbonaceous fiber blended with the hollowthermoplastic fibers. The carbonaceous fibers used in the inventionadvantageous are characterized by having a percentage char value greaterthan 65 and a thermal conductivity of less than about 1 BTU ft/hr ft²°F.

The carbonaceous fibers may themselves be solid, hollow, porous, linearor non-linear in configuration.

The hollow fibers used in the invention preferably are crazed or crackedfor improved insulation value. Also, cracked hollow styrenic fibersprovide the structure a layer volume coverage at lower weight.

The invention also provides a new process for preparing crazed orcracked hollow thermoplastic fibers, particularly styrenic fibers,having improved insulation values characterized by drawing andaspirating or fibrillating the hollow fibers during preparation.

The cracked or crazed hollow fibers of the invention are believed to becharacterized by the following equation: ##EQU2## wherein W is the widthof the fiber;

D₀ is the outside diameter of the fiber, and

n is the number of crazes or cracks,

whereby when for a given D₀ =30 μm

n=4, W is 21.4 μm;

n=6, W is 15 μm;

n=12, W is 7.8 μm.

It has been found that the larger the number of crazes or cracks, thesmaller the fiber width and a reduction in K-factor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with one embodiment of the invention there is provided alightweight batting having a high degree of thermal insulation and goodfire resistance by blending (A) about 20 to 75% by weight, preferably 20to 50% by weight of non-graphitic carbonaceous fibers having an LOIvalue of greater than 40, a char percentage greater than 65 and athermal conductivity of less than 1 BTU ft/hr ft² °F., and (B) hollowthermoplastic fibers, preferably, styrenic fibers. Higher amounts of thecarbonaceous fibers are preferred with the more flammable thermoplasticfibers. A preferred minimum amount of carbonaceous fibers is that whichprovides a synergistic amount of fire resistance so that the insulationpasses the requirements of 14 FAR 25.853(b) for non-flammability. Thecombination also have improved ignition resistance.

Preferred hollow fibers are those having a fiber width of about 6 μm to30 μm and at least 6 cracks or crazes, preferably about 12.

In accordance with another embodiment, the structure of the inventioncan comprise a lightweight structural panel of a compression formedcomposite of a thermoplastic or thermosetting resin matrix containingfrom 10 to 95 percent by weight of the fibrous blend of the invention.The panel can be used alone or in combination with a nonflammablereinforcement scrim comprising, for example, a woven, nonwoven, orknitted fabric, web, foam or a metallic screen or glass screen.

The structures of the present invention provide an improvement overfiberglass structures which utilize phenolic binders. The improvementincludes an advantage in weight as well as in smoke characteristics.

Thermoplastic reins which can be used to form the hollow fibers of theinvention, for example, may include polyethylene, ethylene vinyl acetatecopolymers, polystyrene, polyvinyl chloride, polyvinyl acetate,polymethacrylate, acrylonitrile-butadiene-styrene copolymers (ABS),polyphenylene oxide (PPO), a halo group modified PPO, polycarbonate,polyacetal, polyamide, polysulfone, polyether sulfone, polyolefins,polyacrylonitrile, polyvinylidene chloride, polyvinyl acetate, polyvinylalcohol, polyvinyl pyrrolidone, ethyl cellulose, polyvinyl chlorodivinylacetate copolymer, polyacrylonitrile-styrene copolymer,polyacrylonitrile-vinyl chloride copolymer, styrene,carboxymethylcellulose, polyparaxylene, polyimide, polyamide-imide,polyester imide, polyetherimide, polybenzimidazole, polyoxadiazole, andthe like.

Other suitable thermoplastic materials are disclosed in Modern PlasticEncyclopedia, 1984-1985, Vol. 61, No. 10A, McGraw-Hill, New York, N.Y.

The thermoplastic resins used to form the hollow fibers of the inventionmay contain plasticizer (mineral oil, dioctyl phthalate, etc.), flameretardant (hexabromocyclododecane, decabromodiphenyl oxide, aluminatrihydrate, etc.), acid scavengers (MgO, etc.), and extrusion aid orlubricant (calcium stearate, etc.).

The hollow fibers of the invention can be in any form. The fibers can befibrillated or aspirated hollow fibers, stretched hollow fibers or curlyhollow fibers.

A first group of carbonaceous fibers that can be used in the inventionare classified as being electrically nonconductive and to possess noanti-static characteristics, i.e., they do not have the ability todissipate an electrostatic charge.

The term "electrically nonconductive" as utilized in the presentinvention relates to fibers having an electrical resistance of greaterthan 4×10⁶ ohms/cm when measured on a 6K tow (6000 filaments) formedfrom precursor fibers having a diameter of from 4 to 25 microns. Suchfibers have a specific resistivity of greater than 10⁻¹ ohms cm. Thespecific resistivity is calculated from measurements as described in thepublished European Patent Application Serial number 0199567.

When the precursor fiber is an acrylic fiber it has been found that anitrogen content of greater than 18 percent results in a nonconductivefiber.

In a second group, the carbonaceous fibers are classified as beingpartially electrically conductive (i.e., having low conductivity) andhaving a carbon content of less than 85 percent. Low conductivity meansthat the fibers have a resistance of from 4×10² to 4×10⁶ ohms/cm, asdetermined by the measurements hereinbefore specified. Preferably, thecarbonaceous fibers are derived from stabilized acrylic fibers andpossess a percentage nitrogen content of from 16 to 20 percent for thecase of a copolymer acrylic fiber, more preferably from 18 to 20percent. The structures formed therefrom are lightweight, have lowmoisture absorbency, good abrasive strength together with goodappearance and handle.

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed, sincethese are to be regarded as illustrative rater than restrictive.Variations and changes may be made by those skilled in the art withoutdeparting from the spirit of the invention.

EXAMPLE 1

Following the procedure of U.S. Pat. No. 4,882,223, which is hereinincorporated by reference, polystyrene with a 300,000 weight averagemolecular weight was introduced into a 3/4" extruder. The polymer wasmelted at about 450° F. and passed through a Zenith gear pump at about475° F. The molten polymer was pumped to the pack well and then to apack assembly consisting of a screen and spinneret with low pressure airpassing through the inner hole to produce a hollow fiber. The spinnerethad a temperature of 392° F. and an operating pressure of 400 psi. Thefiber was then passed through draw rolls and was wound around Leesonatake-up rolls with an aspirator device at 400 ft/min.

The aspirator was normally used to "suck" off the fibers while a fullroll was taken off and an empty roll loaded on. Some of the fibers werecollected by passing through the aspirator and into a plastic bag. Inentering the aspirator, the fibers went around a fairly sharp rightangle bend. Once entering into the air stream of the aspirator, thefiber appeared to go through a twisting motion. The fibers were cottonysoft and somewhat like a loose threads instead of brittle fibersproduced without passing it through the aspirator. The individual fibershad a 25˜30 μm outside diameter with a wall thickness of 2-5 μm. Theaspirated fibers has crazes or cracks along the axial direction of thehollow fibers probably due to the twisting motion of individual fiberswhen passing through the aspirator.

EXAMPLE 2

The hollow fibers of Example 1 where then hand cut into two inch lengthand hand blended with carbonaceous fibers and polyester binder fibers.After hand blending, the fiber blend was fed into a Rando Mizer Card tofurther blend and open the fibers. The Rando Mizer Product was processedinto a non-woven batting on a Rando-B machine. The batting wasthermobonded at 225° F. for 60 seconds.

Table 1 shows the K-factors as a function of density and carbonaceousfiber concentration. As a comparison, the fiberglass batt with a densityof 0.65 pcf has a K-factor of 0.315.

                  TABLE 1                                                         ______________________________________                                        K-FACTORS OF FIBER BLEND BATTS                                                NCF/Hollow                     K-Factor                                       Polymer Fiber       Density    BTU in/hr                                      Batt                (pcf)      ft.sup.2 °F.                            ______________________________________                                        Sample 1                                                                      30% NCF*            0.57       0.311                                          20% Polyester binder                                                                              0.85       0.270                                          50% Polystyrene hollow fiber                                                                      1.70       0.231                                          Sample 2                                                                      20% NCF*            0.62       0.302                                          20% Polyester binder                                                                              0.83       0.275                                          60% Polystyrene hollow fiber                                                                      1.24       0.248                                          Sample 3                                                                      12% NCF*            0.52       0.353                                          20% Polyester binder                                                                              0.78       0.304                                          68% Polystyrene hollow fiber                                                                      1.56       0.246                                          Sample 4                                                                      30% NCF*            0.45       0.321                                          20% Polyester binder                                                                              0.68       0.276                                          50% Nylon 8207 hollow fiber                                                                       1.35       0.233                                          Sample 5                                                                      20% NCF*            0.52       0.335                                          20% Polyester binder                                                                              0.69       0.299                                          60% Nylon 8207F     1.04       0.262                                          Sample 6                                                                      10% NCF*            0.79       0.309                                          20% Polyester binder                                                                              1.05       0.283                                          70% Nylon 8207F     1.57       0.255                                          Sample 7                                                                      30% NCF*            0.70       0.298                                          20% Polyester binder                                                                              0.94       0.271                                          50% PET recycle     1.41       0.245                                          Sample 8                                                                      77% NCF*            3.193      0.208                                          23% Polyester binder                                                                              5.602      0.209                                          Sample 9                                                                      20% NCF*            0.359       .401                                          10% Kodel 410 Polyester (2.25d)                                                                   0.539       .335                                          10% Kodel 410 Polyester (8.5d)                                                                    1.078       .264                                          60% Dacron 435 (5.5d)                                                                             2.995       .230                                          Sample 10                                                                     20% NCF*            0.82       0.315                                          20% Polyester binder                                                                              1.09       0.287                                          60% PET recycle     1.64       0.256                                          Sample 11                                                                     Fiberglass          0.65       0.315                                          Example 12                                                                    Polystyrene fiber   1.0        0.337                                          Sample 13                                                                     Aspirated polystyrene                                                                             1.0        0.256                                          Hollow fiber        0.5        0.277                                          ______________________________________                                         *Non-linear nonelectrically conductive carbonaceous fibers derived from       polyacrylonitrile.                                                       

EXAMPLE 3

A general purpose, fiber grade polypropylene (NPP2000-GJ produced byNorthern Petrochemical Co.) with a melt index of 2.0 was extruded at600° F. to produce hollow fibers as in Example 1. The individual hollowfiber had a 28 μm O.D.×22 μm I.D. The aspirated hollow fibers were alsostretched to reduce the diameter and to add curl for bulking and theK-factors are compared in Table 2.

                  TABLE 2                                                         ______________________________________                                                         Density  K (BTU in/hr                                        Fibers           (pcf)    ft.sup.2 °F.)                                ______________________________________                                        Aspirated polypropylene                                                                        1.5      0.237                                               Hollow fibers    1.0      0.259                                                                0.51     0.320                                                                0.26     0.414                                               Hand stretched aspirated                                                                       0.25     0.371                                               polypropylene fibers                                                          ______________________________________                                    

EXAMPLE 4

Special acrylic fiber (SAF) from Cautaulds Ltd. was dissolved inN-methyl pyrrolidone to obtain a 15-45 vol. % solution. The polymer wasthen spun at a temperature between 160° to 200° C. using a 16 hole fiberspinneret and nitrogen as a core gas. The spun hollow fibers were thenquenched in a water bath at about 10° C. for about 2 seconds tocoagulate or phase separate the denser polymer at the surface of hollowfibers squeezing more solvent toward the inner surface. These hollowfibers were then passed through a water bath at about 30° C. to leachout the solvent and to obtain an asymmetric porous structure withgreater porosity toward the inside of the hollow fibers (200μOD/20μID).These asymmetric porous hollow fibers were dried and then heat treatedin a forced air oven at 200° C. for 30 minutes to promote the oxidationand crosslinking reactions of the SAF. This was followed by a heattreatment in an inert atmosphere of nitrogen at 500° C. until an 85%loss of initial polymer sample weight is achieved. The result is anasymmetric porous carbonaceous fiber.

In lieu of N-methyl pyrrolidone there may be utilized as a solventsulfolane, dimethylformamide, polyethylene glycol, polyethylene glycerolor mixtures thereof, for example, 25% polyethylene glycol/75% sulfolane.

In lieu of SAF there may be utilized polyacrylonitrile or itscopolymers.

EXAMPLE 5 Nonflammability Test

The nonflammability of the various blend of the invention weredetermined following the test procedure set forth in 14 CFR 25.853(b).The tests were performed as follows:

A minimum of three 2.5 cm×15 cm×30 cm specimens of each blend wereconditioned by maintaining the specimens in a conditioning roommaintained at temperature of 21° C. ±5° and 50 percent ±5 percentrelative humidity for 24 hours preceding the test.

Each specimen was supported vertically and exposed to a Bunsen or Turillburner with a nominal I.D. tube adjusted to give a flame of 3.8 cm inheight. The minimum flame temperature measured by a calibratedthermocoupled pyrometer in the center of the flame was 843° c. The loweredge of the specimen was 1.9 cm above the top edge of the burner. Theflame was applied to the center line of the lower edge of the specimenfor 12 seconds and then removed. The results of the test is shown inTable 3.

                  TABLE 3                                                         ______________________________________                                        FLAMMABILITY TEST ACCORDING TO FAR.25.853                                                          Burn    Flame Drip  Pass                                 Sample                                                                              Sample         Length  Time  Time  or                                   No.   Composition    (in)    (sec) (sec) Fail                                 ______________________________________                                        1     30% NCF*       3        <5   0     Pass                                       20% Polyester                                                                 50% Polystyrene                                                               .sup.      hollow fiber                                                 2     20% NCF*       5.5     <15   0     Pass                                       20% Polyester                                                                 60% Polystyrene                                                               .sup.      hollow fiber                                                 3     12% NCF*       10.0     25   0     Fail                                       20% Polyester                                                                 68% Polystyrene                                                               .sup.      hollow fiber                                                 4     30% NCF*       1.5      <5   0     pass                                       20% Polyester                                                                 50% Nylon 8207F                                                               .sup.      hollow fiber                                                 5     20% NCF*       2.0      <5   0     Pass                                       20% polyester                                                                 60% Nylon 8207F                                                               .sup.      hollow fiber                                                 6     10% NCF*       3.0      <5   0     Pass                                       20% Polyester                                                                 70% Nylon 8207F                                                               .sup.      hollow fiber                                                 7     30% NCF*       1.5     <10   0     Pass                                       20% Polyester                                                                 50% PET** recycled                                                            .sup.      hollow fiber                                                 8     20% NCF*       1.0       0   0     Pass                                       20% Polyester                                                                 60% PET** recycled                                                            .sup.      hollow fiber                                                 ______________________________________                                         *Non-linear nonelectrically conductive carbonaceous fibers derived from       polyacrylonitrile.                                                            **Polyethylene terephthalate                                                  Polyester: Celanese Polyester 353 binder (4 denier)                           Polyester: 300,000 Molecular weight                                      

EXAMPLE 6 Preparation of Crimped Expanded Carbonaceous Fibers

A copolymer comprising 95% acrylonitrile and 5% vinyl chloride wasdissolved in acetone. To this copolymer solution, 40% of1,1,2-trichloro-1,2,2-trifluoroethane and 0.2% titanium dioxide wereadded to have the final polymer concentration adjusted to 35%; and thesolution was stirred at 40° C. to yield a spinning solution. Thissolution was then discharged into a 20% aqueous solution of acetone at35° through a spinneret with 10000.10 mm φ slits. After immersiontherein for 9 seconds at a take-up rate of 4.5 m/min., the spun mix wasimmersed for 6 sec. in a 25% aqueous acetone solution at 30° C. whiledrawing it 1.8 times, and thereafter, crimped and heat treated at 525°C. without any tension or stress in an apparatus described inapplication Ser. No. 340,098. The fiber when carbonaceous had lowelectrical conductivity, an expansion of about 10%, a reversibledeflection ratio greater than 2:1 and an LOI greater than 40.

To prepare the linear fibers, the crimping step may be omitted.Similarly, there may be prepared expanded carbonized polybenzimidazolefibers.

EXAMPLE 7

Expanded KEVLAR polyamide continuous 3K tow was prepared according toU.S. Pat. No. 4,752,514 having nominal single fiber diameters of 15micrometer. The tow was knit on a circular knitting machine into a clothhaving from 3 to 4 loops per centimeter. The cloth was heat set at 525°C. for two minutes. When the cloth was deknitted, it produced a towwhich had an elongation or reversible deflection ratio of greater than2:1. The deknitted tow was cut into various lengths of from 5 to 25 cm,and fed into a Platt Shirley Analyzer. The fibers of the tow wereseparated by a carding treatment. The fibers can be blended with hollowstyrenic fibers to produce a light weight insulation.

EXAMPLE 8

A 3K tow of expanded p-aramid was knit on a circular knitting machine ata rate of 4 stitches/cm and was then heat treated at a temperature of425° C. without stabilizing for ten minutes. The cloth was deknitted andthe two (which had an elongation or reversible deflection ratio ofgreater than 2:1) was cut into 7.5 cm lengths. The cut tow was thencarded on a Platt miniature carding machine together with the fibers ofExample 1 to produce a resilient compressible fluff.

The fluff can be densified by needle punching, treated withthermoplastic binder such as a polyester binder, or the like, to form amat or felt-like structure.

EXAMPLE 9

Following the procedure of Example 1, the following hollow fibers withabout 6-12 cracks were prepared:

    __________________________________________________________________________            Spinneret                                                                           Spinneret                                                                           Take-up                                                                             Fiber Wall                                                  Temp. Pressure                                                                            Speed ID    Thickness                                     Polymer (°C.)                                                                        (psi) (ft/min)                                                                            (micron)                                                                            (micron)                                      __________________________________________________________________________    Polystyrene                                                                           290˜295                                                                       380˜440                                                                       320˜500                                                                       45˜55                                                                          5˜7                                    Nylon 8207F                                                                           310   970   500˜1000                                                                      35˜50                                                                          4˜8                                    PET Recycle                                                                           270   370   500   30˜40                                                                          7˜9                                    Polypropylene                                                                         321   460˜500                                                                       350   65     5                                            PETG    290   340˜490                                                                       500   45˜50                                                                          4˜5                                    Polyester                                                                             360   420   140˜176                                                                       75    10                                            __________________________________________________________________________     Polystyrene: Dow Chemical Company                                             Nylon 807F: AlliedSignal                                                      PET Recycle: Star Plastics                                                    Polypropylene: Norchem PP 7300KF                                              PETG: Eastman Kodak                                                           PE 529: Dow Chemical Company                                             

What is claimed:
 1. A structural panel of a compression formed compositecomprising a thermoplastic or thermosetting resin and from about 10 to95 percent by weight of an intimate blend of A) 20 to 75% by weight ofnon-electrically conductive carbonaceous fibers derived from oxidizedpolyacrylonitrile fibers and B) hollow styrenic fibers having about 6 to12 crazes along the axial direction of the fibers, said carbonaceousfibers having an LOI value greater than 40, a percent char value greaterthan 65, a carbon content of less than 85 percent and a thermalconductivity less than 1 BTU ft/hr ft² °F.
 2. The structural panel ofclaim 1, wherein said carbonaceous fibers are derived from a stabilizedexpanded acrylic fiber selected from acrylonitrile homopolymers,acrylonitrile copolymers and acrylonitrile terpolymers, wherein aidcopolymers and terpolymers contain at least 85 mole percent acrylicunits.
 3. The structural panel of claim 1, wherein said carbonaceousfibers have a carbon content of less than 85 percent.
 4. The structuralpanel of claim 1, wherein the carbonaceous fibers are a mixture oflinear and non-linear expanded carbonaceous fibers.